943 research outputs found
Gravitational Cherenkov Radiation from Extended Theories of Gravity
We linearize the field equations for higher order theories of gravity that
contain scalar invariants other than the Ricci scalar. We find that besides a
massless spin-2 field (the standard graviton), the theory contains also spin-0
and spin-2 massive modes with the latter being, in general, ghost modes. The
rate at which such particles would emit gravitational Cherenkov radiation is
calculated for some interesting physical cases.Comment: 6 pages, to appear in Mod. Phys. Lett. A. arXiv admin note: text
overlap with arXiv:0911.3094, arXiv:1105.619
The Missing Matter Problem: From the Dark Matter Search to Alternative Hypotheses
Dark matter is among the most important open problems in both astrophysics
and particle physics. We review the status of art of dark matter search at
theoretical and experimental level discussing also alternative hypotheses
Parasitismo de Telenomus remus em ovos de Spodoptera frugiperda e Corcyra cephalonica.
Objetivou-se avaliar as características biológicas de T. remus criado em ovos do hospedeiro alternativo C. cephalonica comparando-se ao hospedeiro natural S. frugiperda. O experimento foi conduzido em sala climatizada (T: 25±2°C; UR: 70±10%; Fotofase: 12h), com delineamento inteiramente casualizado sendo dois tratamentos (hospedeiros) e 20 repetições. Em tubos de vidro de fundo chato, foram colocados 30 ovos parasitados de S. frugiperda. Após a emergência dos adultos (24h), aproximadamente 100 ovos inviabilizados de C. cephalonica e aproximadamente 100 ovos de S. frugiperda, foram colados com cola atóxica (30%) em cartelas de papel e oferecidos aos parasitoides. O parasitismo foi permitido por 24h. Os parâmetros biológicos avaliados foram: porcentagem de parasitismo; viabilidade e razão sexual. As porcentagens de parasitismo (92,64% e 48,27%) e viabilidade (96,79% e 89,14%) apresentaram diferença significativa, já a razão sexual (0,78 e 0,68 fêmeas) não diferiu entre os hospedeiros S. frugiperda e C. cephalonica, respectivamente. O menor parasitismo verificado em ovos do hospedeiro alternativo pode ser atribuído ao fato do parasitoide ser criado por sucessivas gerações em ovos do hospedeiro natural em contrapartida, a alta viabilidade nos ovos de C. cephalonica (>80%) indica um hospedeiro potencial para criações massais de T. remus. Assim, para que o hospedeiro alternativo possa ser utilizado com sucesso, fazem-se necessários estudos de T. remus criados por sucessivas gerações em ovos de C. cephalonica
Relativistic orbits and Gravitational Waves from gravitomagnetic corrections
Corrections to the relativistic theory of orbits are discussed considering
higher order approximations induced by gravitomagnetic effects. Beside the
standard periastron effect of General Relativity (GR), a new nutation effect
was found due to the orbital correction. According to
the presence of that new nutation effect we studied the gravitational waveforms
emitted through the capture in a gravitational field of a massive black hole
(MBH) of a compact object (neutron star (NS) or BH) via the quadrupole
approximation. We made a numerical study to obtain the emitted gravitational
wave (GW) amplitudes. We conclude that the effects we studied could be of
interest for the future space laser interferometric GW antenna LISA.Comment: 6 pages, 10 figures; Multifrequency Behaviour of High-Energy Cosmic
Sources, Vulcano Workshop 200
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Retrofit 2050:Critical challenges for urban transitions
Scaling up retrofit presents a number of critical challenges for the transition
to urban sustainability. Drawing together insights from the EPSRC Retrofit
2050 project this briefing sets out key success factors that need to be in place
to deliver sustainable futures for UK cities
Jeans analysis of self-gravitating systems in f(R)-gravity
Dynamics and collapse of collisionless self-gravitating systems is described
by the coupled collisionless Boltzmann and Poisson equations derived from
-gravity in the weak field approximation. Specifically, we describe a
system at equilibrium by a time-independent distribution function
and two potentials and solutions of the modified
Poisson and collisionless Boltzmann equations. Considering a small perturbation
from the equilibrium and linearizing the field equations, it can be obtained a
dispersion relation. A dispersion equation is achieved for neutral
dust-particle systems where a generalized Jeans wave-number is obtained. This
analysis gives rise to unstable modes not present in the standard Jeans
analysis (derived assuming Newtonian gravity as weak filed limit of ).
In this perspective, we discuss several self-gravitating astrophysical systems
whose dynamics could be fully addressed in the framework of -gravity.Comment: 8 pages, 2 figures, Accepted for publication in PR
Life-History and Behavior of the Diamondback Moth Plutella xylostella on Brassicaceae Cultivars over Multiple Generations
The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a cosmopolitan pest that causes leaf-area reduction in Brassicaceae plants. DBM populations have significant genetic variability that manifests in different feeding preferences and reproductive behaviors across generations. We evaluated the influence of Brassicaceae cultivars on biological and behavioral parameters across 18 generations of DBM populations that were separated and held on three varieties of Brassicaceae: Brassica oleracea var. acephala (kale), Brassica oleracea var. italica (broccoli), and Brassica oleracea var. capitata (cabbage). P, F6, F12, and F18 generations were evaluated, and biological aspects of young adulthood and fertility parameters of adults held on each host plant were examined over multiple generations. Additionally, larvae and adults were subjected to dual-choice and multiple-choice (feeding and oviposition) between cultivars, over generations. The results indicated that larvae of P. xylostella consumed greater quantities of kale and broccoli cultivars, on average (4.05 cm2), than cabbage (2.7 cm2). The number of eggs per female in F18 generation was 1.95 and 2.17 times higher than those in the parental (P) generation, when reared on kale and cabbage. The population reared exclusively on kale had higher net population growth rate (R0), intrinsic rate (rm), finite rate (λ) and generation time (T) than that reared on broccoli and cabbage. Last generations evaluated, the larval stage reared on cabbage showed feeding preference (F18) and oviposition preference (F12 and F18) for cabbage. Thus, we note the existence of learning, characterized as pre-imaginal conditioning to cabbage cultivars, over various DBM generations
Using space-VLBI to probe gravity around Sgr A*
The Event Horizon Telescope (EHT) will soon provide the first high-resolution
images of the Galactic Centre supermassive black hole (SMBH) candidate
Sagittarius A* (Sgr A*), enabling us to probe gravity in the strong-field
regime. Besides studying the accretion process in extreme environments, the
obtained data and reconstructed images could be used to investigate the
underlying spacetime structure. In its current configuration, the EHT is able
to distinguish between a rotating Kerr black hole and a horizon-less object
like a boson star. Future developments can increase the ability of the EHT to
tell different spacetimes apart. We investigate the capability of an advanced
EHT concept, including an orbiting space antenna, to image and distinguish
different spacetimes around Sgr A*. We use GRMHD simulations of accreting
compact objects (Kerr and dilaton black holes, as well as boson stars) and
compute their radiative signatures via general relativistic radiative transfer
calculations. To facilitate comparison with upcoming and future EHT
observations we produce realistic synthetic data including the source
variability, diffractive and refractive scattering while incorporating the
observing array, including a space antenna. From the generated synthetic
observations we dynamically reconstructed black hole shadow images using
regularised Maximum Entropy methods. We employ a genetic algorithm to optimise
the orbit of the space antenna with respect to improved imaging capabilities
and u-v-plane coverage of the combined array (ground array and space antenna
and developed a new method to probe the source variability in Fourier space.
The inclusion of an orbiting space antenna improves the capability of the EHT
to distinguish the spin of Kerr black holes and dilaton black holes based on
reconstructed radio images and complex visibilities.Comment: 15 pages, 14 figures, A&A accepte
Position and frequency shifts induced by massive modes of the gravitational wave background in alternative gravity
Alternative theories of gravity predict the presence of massive scalar,
vector, and tensor gravitational wave modes in addition to the standard
massless spin~2 graviton of general relativity. The deflection and frequency
shift effects on light from distant sources propagating through a stochastic
background of gravitational waves, containing such modes, differ from their
counterparts in general relativity. Such effects are considered as a possible
signature for alternative gravity in attempts to detect deviations from
Einstein's gravity by astrophysical means.Comment: 9 pages, 1 figur
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